Electric Dipole for IIT JEE Physics

Electric Dipole Moment for JEE Mains and Advance

Introduction

In each and every single particle that surrounds us, there is a presence of electricity. Our body also has an electric charge. 
There are a lot of examples to confirm this phenomenon. One of the examples is to take a towel and vigorously rub a comb over it and then bring it near to the hair. You will be amazed to see that the electric ions generated as the result will get attracted towards the comb.

This happens due to the production of an electric charge. Here, in this article we are going to interpret the performance and reaction of opposite electric charges when they are kept near to each other. The entire concept is called as the Electric Dipole. It is a significant element of electrostatics.

So, the first thing that comes to our mind is what an electric dipole is. It is a phenomenon that shows separation of negative and positive charges. An electret is referred to as the stable form of an electric dipole. One of the simplest ways to understand an electric dipole is to get a set of electric charges that carry the same magnitude but have opposite signs. These charges are separated by a small distance.

What type of electric field is formed as a result of an electric dipole?

Now let us see the kind of electric field created by an electric dipole. The electric field formed due to an electric dipole created between a pair of positive (+q) charge and negative (-q) charge can be determined easily from the law of Coulomb and Superposition. The field generated due to an electric dipole is referred as the dipole field.

The electric field caused by an electric dipole at any given point of time on the axis of the electric dipole is determined as:
When the referring point is present in the equatorial axis of an electric dipole and is vertical to the axis that passes through the midpoint, the total electric field caused due to an electric dipole is the vector sum of the entire electric field generated by q and –q charges.

One of the important things that need to be noted when measuring an electric dipole is that the reason why the direction of it is always from the negative to the positive. This is because the positive electric charge of an electric dipole is deterred by the positive electric charge of the electric field. At this time, the positive electric charge will get attracted towards the negative electric charge of the electric field. In the same way, the resulting direction of Force is “-qE”. F=qE ----(1)
It is the product of the negative electric charge of the electric dipole and the positive side of the electric field. The above equation makes it clear that the force of attraction pulls the negative charge of the dipole towards the positive Electric field.

What is an electric dipole moment?

A system that consist of a negative and positive charge of same magnitude q, and set apart from each other by a distance ‘d’ is referred to as an electric dipole. With this definition of an electric dipole, a new vector is concluded. It is called as the electric dipole moment.

Suppose the magnitude of each of these charges is q, and the distance measured from the midpoint of the positive electric charge to the midpoint of the negative charge is d, then product “qd” will be described as the “electric dipole moment”. Electric dipole moment is defined as “p”. So, here p = qd. The direction of vector is from the negative electric charge to the positive electric charge.

How can an electric dipole moment can be useful in scientific application?

Electric dipole moment has several important applications in the field of science. It is a useful concept when impact of the separation of microscopic charge is noticeable, but the real distance between these charges is very small for calculation.
It has been seen that most of the molecules have permanent electric dipole moments. Molecules and atoms that do not have a permanent electric dipole moment can obtain one when they are kept in an external electric field.

The potential generated by an “electric dipole moment” is measured by adding the potential of the positive and negative charges that generates it. So, putting in simple words, an electric dipole moment is defined as the precise measurement of the strength linked with any electric dipole.

Performing a study on electric dipole assists in getting a good understanding of the applications and performance of polar molecules. These are the molecules that have a permanent electric dipole moment even without establishing any contact with an electric field. In most of the molecules, the mid-region of a negative charge and positive charge coincide, and so the value of their electric dipole moment is zero.

What is defined as an ideal electric dipole?

An ideal condition of an electric dipole is determined when a pair of the same magnitude but opposite charges are placed at a small vector distance, then they form an electric dipole. The ideal dipole comprises of two very large sized charges (+ q) and (- q) that are separated by a very small distance.

What is the application of an electric dipole?

Electric dipole is defined as a set of point charges that have opposite charges of equal magnitude and separated by a fixed distance. There are several physical systems that use this concept for their operations. Water molecules and an antenna of a television are some good examples of an electric dipole.

There is a lot of physical significance of an electric dipole. Besides electrostatics, an electric dipole has a lot of importance in chemistry, too. As seen in most of the molecules, the midpoint of a positive and a negative charge meets at one point, that implies the distance present between both these charges is zero. This makes the dipole moment to becomes 0.

Carbon dioxide and Methane are the two compounds that fall in this category of 0 dipole moment. Such kind of molecules are referred to as non-polar molecules. These molecules build an electric dipole when they come in contact of an electric field.
The molecules that have a permanent and stable dipole moment that is defined as the mid region of a negative and a positive charge do not coincide. These molecules are referred to as polar molecules. One of the best examples of a polar molecule is water or H2O.

How would you define an electric dipole moment, a scalar or a vector quantity?

“Electric dipole moment” (p) is calculated as “the product of the distance between the charges of different polarity and the equal magnitude of them”. It is a vector quantity and the direction of it is denoted from the (-) electric charge to the (-) electric charge. The unit of an electric dipole moment is coulomb meter.

The dimension of electric dipole moment is the same as the dimension of electric current length time. The SI unit of it is ampere meter second.

How do you define electric dipole moment of molecules?

Dipole moments in any molecule is responsible for the performance of a substance when seen in contact of an external electric field. The electric dipoles get aligned to an external field that can be either dependent on time or constant.

This outcome forms the foundation of a current experimental method called as “dielectric spectroscopy”. Dipole moments are present in water molecules, and bio-molecules like proteins.

How do you determine the formula of a dipole moment?

When seen in SI, the actual unit of dipole moment is “C.m” (columb.meter). This is very large to be applied on a molecular scale. It is defined as the product of charge of ions and the distance between them. So, the dimensional formula for an electric dipole is calculated as p=qd.
Where,
p is the electric dipole moment,
q is the charge, and
d is the distance that separates the two opposite charged ions of the same magnitude.

How are the bond dipole moments defined?

Bond dipole moment is measured in “debyes”. It is represented as D and its value is obtained by calculating the charge in the form of static coulomb and multiplying it with the distance “d” measured in Angstroms.

What do you mean by the net dipole?

As dipole moment is considered to be a vector quantity, it comprises of magnitude as well as direction. The two atoms C and O, present inside a “CO” molecule can have varying polarities but the resultant molecule is non-polar. This is because the 2 dipole moments behave against one another. This leads to zero net dipole.

In what ways does a magnetic dipole differs from an electric dipole?

The term electric dipole moment helps in the measurement of the separation of negative and positive charges in the electric system. In a magnetic dipole moment, the magnetic dipole is represented by the total amount of torque that is produced by any material present in a magnetic field.

The value of the magnetic dipole is calculated as the product of strength of the pole and the distance present between the poles.

Can a magnet be considered as a dipole?

A “dipole magnet” is basically a magnet that has two poles, North and South. These poles are located at the opposite ends of it and are oppositely charged to each other. This polarity of the charges makes them the best and the simplest example of a bar magnet.